The present invention is directed generally to micro-electromechanical system (MEMS) devices and, more particularly, to MEMS devices constructed from alternating layers of metal and a sacrificial material.
MEMS devices are typically constructed using traditional CMOS processing techniques. Such processing techniques are well developed as they are used to fabricate many different types of integrated circuits such as memory devices, processors, logic circuits, to name a few. As a result, the construction of MEMS devices is advanced whenever there are improvements in CMOS processing techniques.
In fabricating a typical MEMS device, various layers of material are formed on a substrate and etched according to a pattern to form the desired device(s). The resulting device is typically formed of a composite of various layers of materials. The device is then released from the substrate by removing a portion of the substrate from under the device. MEMS devices constructed using such techniques include, for example, beams of various design used for accelerometers, switches, variable capacitors, sensors, to name a few, and flexible meshes used for capacitors, microspeakers and microphones.
When devices are comprised of composite structures, the different materials comprising the composite structure respond to thermal and other types of stress differently, which may cause the structure to bend or fail prematurely. Releasing the device by removing a portion of the substrate requires close control over process parameters to insure that the right amount of substrate is removed. Under-etching, and the device may not be released; over-etching and the device may have characteristics that vary from what was designed and expected. Thus, the need exists for a process that is easy to implement with CMOS processing techniques and that allows for devices to be constructed of a single material in a simple, easily repeatable manner.